In non-invasive imaging systems, x-ray tubes are used in various x-ray systems and computed tomography (CT) systems as a source of ionizing (x-ray) radiation. The ionizing radiation is emitted in response to control signals during an examination or imaging sequence. An emitter within the cathode emits a stream of electrons in response to heat resulting from an applied electrical current, and/or an electric field resulting from an applied voltage to a properly shaped metallic plate in front of the emitter. The anode includes a target that is impacted by the stream of electrons. The target, as a result of impact by the electron beam, produces x-ray radiation to be emitted toward an imaged volume. In such imaging systems, a portion of the radiation passes through a subject of interest, such as a patient, baggage, or an article of manufacture, and impacts a digital detector or a photographic plate where the image data is collected. The signals are then processed to generate an image that may be displayed for review. In other systems, such as systems for oncological radiation treatment, a source of x-rays is used to direct ionizing radiation toward a target tissue. Regardless of the type of x-ray system used, it is beneficial to know the amount (dose) of x-ray exposure during individual imaging or treatment events.
Accordingly, one concern with ionizing radiation includes an increased likelihood of harm or injury associated with radiation-induced injury to the tissue of the exposed subject. A variable that affects a likelihood of causing radiation-induced injury to tissue of an exposed subject is the dose or amount of radiation absorbed by the exposed subject. Variables that affect a dose of radiation absorbed by the exposed subject include a rate of delivery of radiation, a time of exposure of radiation, a fraction of radiation absorbed by the exposed subject, age, or other characteristics of the exposed subject, and location of radiation exposure on the exposed subject. Another concern with use of ionizing radiation includes an increased likelihood of causing effects (e.g., radiation—induced cancers) to the exposed subject.